Comfort heat exchanger

ABSTRACT

A heat exchanger, especially a heat exchanger in the form of a comfort heat exchanger, is disclosed. The heat exchanger is comprised of two manifold elements adapted to receive and discharge fluid, and a plurality of tube units transversely located between the manifolds, each tube unit being integrally connected to substantially rigid end elements that fit into the manifolds. The tubes are preferably oriented and expanded to about their original diameter. The heat exchanger is intended to be fabricated from polymer, especially polyamide compositions. The tube units are intended to be manufactured using injection moulding techniques, and then subjected to orientation and expansion steps. Parts fabricated during manufacture of the heat exchangers are also disclosed. The heat exchangers are particularly intended for use as comfort heat exchangers in automobiles.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates to heat exchangers, especially toso-called comfort heat exchangers, and in particular to comfort heatexchangers of the type used in the heating and air conditioning systemsof automobiles.

Heat exchangers are used in a wide variety of end-uses. In someinstances, the heat exchangers are large and the weight of the exchangeris only of minor importance. However, in other instances the size andweight of the heat exchanger is a significant factor. An example of thelatter is in the automobile industry where there are strict anddemanding operating requirements that the exchanger must meet but whereboth the size and weight of the exchanger are important, especially asthe automobile manufacturing companies continue to seek to improve fuelefficiency by reducing the weight of automobiles.

One of the means to reduce the weight of heat exchangers is to fabricatethe exchanger from polymeric material instead of from metal. However, ingeneral, it is not possible to merely substitute polymer for metal.Fabrication techniques that have proven to be quite acceptable usingmetals tend to be inapplicable to polymers. Moreover, performancerequirements tend to mean that many polymers may not be suitable for usein the form of heat exchangers.

With respect to automobiles, there are five types of heat exchangersthat may be used viz. the engine coolant heat exchanger (which isusually referred to as the radiator), air conditioning radiator, oilcooling system, air intake after-cooler or intercooler for turbo-chargedair intake systems and the system used to heat and/or air condition thevehicle i.e. the so-called comfort heat exchanger. Each system hasdifferent performance requirements, including with respect to heat andpressure and with respect to the type of fluid to be passed through oraround the heat exchanger.

A heat exchanger, and parts thereof, fabricated from a thermoplasticpolymer and of a type suitable for use as a comfort heat exchanger in anautomobile or other vehicle has now been found.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an article manufactured froma thermoplastic polymer, said article essentially comprising a pluralityof transverse parallel hollow tubes integrally connected at each end toa substantially rigid end element, each of said end elements havingplanar sides and opposing faces, the tubes being integrally connected toone face of each end element, each of said tubes being radiused at theintegral junction of tube and end element, said end elements havingorifices therein extending between said opposite faces and being influid flow communication with said hollow tubes, said orifices and theinside of said hollow tubes being of uniform cross-section and the wallsof said tubes between the flared junctions being of uniform thickness.

The present invention also provides a device manufactured from athermoplastic polymer, said device essentially comprising a plurality oftransverse parallel hollow tubes integrally connected at each end to asubstantially rigid end element, each of said end elements having planarsides and opposing faces, the tubes being integrally connected to oneface of each end element, each of said tubes being flared at theintegral junction of tube and end element, said end elements havingorifices therein extending between said opposite faces and being influid flow communication with said hollow tubes, and the hollow tubeshaving been oriented to increase the length thereof by at least twotimes, the walls of said tubes between the integral junctions being ofsubstantially uniform thickness.

In a preferred embodiment of the device of the present invention, theinternal diameter of the oriented tubes is at least 0.5 times that ofthe tubes prior to orientation.

In another embodiment, the hollow tubes have been oriented to increasethe length thereof by at least two times and then expanded so that theinternal diameter of said tubes is at least 0.5 times the diameter ofthe tubes prior to orientation.

The present invention further provides a process for the manufacture ofa device from a tubular article formed from a thermoplastic polymer,said process comprising:

(i) inserting rods into the tubes of the tubular article, said articlehaving a plurality of transverse parallel hollow tubes integrallyconnected at each end to a substantially rigid end element, each of saidend elements having planar sides and opposing faces, the tubes beingintegrally connected to one face of each end element, each of said tubesbeing flared at the integral junction of tube and end element, said endelements having orifices therein extending between said opposite facesand being in fluid flow communication with said hollow tubes, the wallsof said tubes between the integral junctions being of substantiallyuniform thickness, said rods having a diameter that is not greater thanthe internal diameter of the tubes;

(ii) placing the article containing the rods into a heated atmosphereand uniformly heating the article to a temperature above the glasstransition temperature but below the melting point of the polymer:

(iii) moving one end element relative to the other end element so as toorient the tubes to a length that is at least two times the length priorto orientation;

(iv) heat setting the oriented tubes; and

(v) cooling the thus oriented and heat set tubes.

In a preferred embodiment of the process of the present invention, thetubes of the tubular article in step (i) are unoriented tubes.

In another embodiment of the process, the article has been formed in aninjection moulding process.

In a further embodiment of the process, the rods are heated prior tostep (iii) of the process.

In addition, the present invention provides a heat exchanger comprising:

(a) two manifold elements, said manifold elements being adapted toreceive and discharge a fluid, and

(b) a plurality of tube units transversely located between saidmanifolds, each of said tube units essentially comprising a plurality oftransverse parallel hollow tubes integrally connected at each end to asubstantially rigid end element, each of said end elements having planarsides and opposing faces, the tubes being integrally connected to oneface of each end element, each of said tubes being radiused at theintegral junction of tube and end element, said end elements havingorifices therein extending between said opposite faces and being influid flow communication with said hollow tubes, the hollow tubes havingbeen oriented to increase the length thereof by at least two times, thewalls of said tubes between the integral junctions being ofsubstantially uniform thickness, said tube units being positioned sothat the hollow tubes are in a spaced apart but juxtaposed relationship,said tubes units being sealed together so that fluid will flow from onemanifold to the other manifold through the hollow tubes.

In a preferred embodiment of the heat exchanger of the presentinvention, the internal diameter of said tubes is at least 0.5 times thediameter of the tubes prior to orientation.

In another embodiment, the thickness of the walls of said tubes is lessthan 0.5 mm, and especially in the range of 0.12-0.4 mm.

In a further embodiment, the outside diameter of the tubes is in therange of 2-7 mm.

In yet another embodiment, the heat exchanger is adapted so that fluidwill flow from an inlet section of a first manifold, through tubes to asecond manifold, and then back through further tubes to an outletsection of the first manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention relates to so-called heat exchangers and to thefabrication of such heat exchangers and will be described withparticular reference to the embodiments shown in the drawings, in which:

FIG. 1 is a schematic representation of a article used in thefabrication of the tube units for the heat exchanger;

FIG. 2 is a cross-section of the article of FIG. 1 taken through endelement 2;

FIG. 3 is a schematic representation of the article of FIG. 1 afterorientation;

FIG. 4 is a schematic representation of the article of FIG. 1 afterorientation and expansion; and

FIG. 5 is a schematic representation of a comfort heat exchanger, shownas an expanded view.

FIG. 6 is an alternative representation to FIG. 5.

With reference to FIG. 1, article 1 is comprised of end elements 2 and 3and hollow tubes 4. There are a plurality of hollow tubes 4 which wouldnormally be of similar shape and size but in embodiments could bedifferent. A plurality of hollow tubes 4 are transversely locatedbetween end element 2 and end element 3. The article, which is intendedto be injection moulded and then used in the fabrication of a heatexchanger, would normally have a plurality of transverse hollow tubese.g. at least four tubes and especially 414 10 tubes, it beingunderstood that the actual number of hollow tubes in the article of FIG.1 will depend in particular on the design of the heat exchanger.

Each end of each hollow tube 4 is radiused on the outside of the tube atthe integral junction 5 of the hollow tube and end element. Theradiusing of the integral junction between the outside of the hollowtube and the end element is the forming of the outside surface of theintegral junction to approximate that of the radius of a circle, as willbe appreciated by those skilled in the art. Such radiusing is importantin order to provide strength to the area at which the hollow tube andend element are joined, especially after the fabrication steps describedhereinafter have been performed and in the subsequent use of the heatexchanger. In embodiments of the invention, the integral junction 5 isboth radiused and flared.

Hollow tubes 4 have a uniform wall thickness between the radiusedelements at integral junction 5. Moreover, hollow tubes 4 are in aspaced apart relationship and are parallel to each other. It ispreferred that hollow tubes 4 be linear and of uniform dimensionthroughout their length, apart from the radiused elements at junctions5. Although hollow tubes 4 are spaced apart, it is preferred that thetubes be juxtaposed to each other but spaced apart in a manner thatwould not substantially restrict the flow of air between the tubes. Thehollow tubes 4, in the embodiment shown in FIG. 1, are positioned atright angles to end elements 2 and 3.

End elements 2 and 3 extend beyond hollow tubes 4 in both directions inthe embodiment shown in FIG. 1, in order to provide a means tofacilitate the assembly of a heat exchanger as described herein. Theextended portions of the end elements, identified as ends 6 in thedrawing, are shown as having lugs 7 and 8 to facilitate such positioningof the device.

A cross-section of FIG. 1 taken through end element 2 is shown in FIG.2. End element 2 is shown as having a plurality of orifices 9, whichcorrespond to the hollow tubes 4 (not shown). Orifices 9 are in fluidflow communication with hollow tubes 4. Moreover, orifices 9 are alignedwith the interior of hollow tubes 4 and in embodiments are of the samecross-sectional shape as hollow tubes 4. It is preferred that orifices 9have a circular cross section.

It is also preferred that end elements 2 and 3 have an elongated shape,as shown in FIG. 2. As shown, the sides 10 are planar and parallel toeach other, to facilitate assembly of a plurality of devices so that theend elements are in a column with side 10 of one end element in abuttingrelationship with side 10 of the end element of the adjacent device inthe heat exchanger. As discussed below, it the articles afterorientation of tubes, be sealed in a manner that does not permit theflow of fluid therebetween. Although the end elements shown in FIG. 2are elongated with parallel sides, it is to be understood that othercross-elemental shapes are possible e.g. hexagonal, a primaryconsideration being ease of final assembly of the heat exchanger.

In an embodiment of the present invention, the distance between lugs 7and 8 and the nearest hollow tube 4 is different on the two ends of theend element, especially by an amount that is approximately equal to halfof the spacing between the axes of adjacent hollow tubes. Such anoff-set nature of the hollow tubes 4 permits alternating assembly of thedevices in the heat exchanger, so that the hollow tubes 4 of one deviceare positioned opposite the gaps between the hollow tubes 4 of theimmediately adjacent device, thereby permitting maximum contact betweenair flowing between tubes and the surfaces of tubes.

It is intended that the article shown in FIGS. 1 and 2 be manufacturedas an integral unit in an injection moulding process. Techniques forsuch manufacture will be understood by those skilled in the art.

FIG. 3 shows a device similar to the article of FIGS. 1 and 2 exceptthat hollow tubes 4 are shown as oriented tubes 11. Oriented tubes 11have a length significantly longer than hollow tubes 4, especially atleast twice as long and in particular 3-5 times longer, and are formedby orientation of the hollow tubes of the article of FIGS. 1 and 2 bycorresponding amounts. Oriented tubes 11 have a wall thickness and anoutside diameter significantly smaller than those of hollow tubes 4, byamounts that are related to the degree of orientation and theconditions/ under which the orientation was conducted. Oriented tubes 11are connected to the radiused portion of hollow tubes 4 at neck 12; asshown in FIG. 3, the radiused portion of hollow tubes 4 does not undergoorientation which is advantageous in the retention of the strength ofthe integral junction 5 between the radiused portion of the hollow tubes4 and end elements 1 and 2.

As noted above, the device shown in FIG. 3 may be formed by orientationof the article of FIGS. 1 and 2. For instance, end elements 1 and 2 maybe clamped and at least hollow tubes 4 heated to a temperature above theglass transition temperature of the polymer from which the device hasbeen formed, to facilitate orientation of hollow tubes 4. End elements 1and 2 are then moved further apart, thereby resulting in orientation ofthe hollow tubes 4 to form oriented tubes 11. Uniformity of heating ofhollow tubes 4, uniformity of the thickness of the walls of the hollowtubes 4 and a smooth orientation step are all important factors in theformation of oriented tubes 11 having acceptable properties.

FIG. 4 is similar to FIG. 3, except that the device shown ischaracterized by hollow tubes that have been oriented, as in FIG. 3, andthen subjected to an expansion step so that the tubes, expanded tubes13, have a diameter more closely related to that of the hollow tubes 4shown in FIG. 1. In particular, expanded tubes 13 have a diameter thatis at least 0.5 times and especially 0.5-1.5 times that of the hollowtubes 4 of FIG. 1. The device of FIG. 4 is formed from the device ofFIG. 3 by applying pressure, e.g. of a gas or liquid to the inside oforiented tubes 12 or by means of a tapered rod or the like inserted intoorifices 9, under conditions that result in expansion of oriented tubes11. Such conditions will include heating the tubes above the glasstransition temperature of the polymer but below the temperature at whichcreep of the polymer or other effects occur that result in the loss ofthe degree of orientation of the polymer, as well as the application ofsufficient pressure under controlled conditions to effect the expansionof the polymer. The tubes after orientation and expansion will usuallybe substantially circular in cross-section but, depending on the shapeand uniformity of cross-sectional thickness of the tubes prior toorientation and/or expansion, such tubes may be other convenient shapescommensurate with acceptable fabrication of the heat exchangers andacceptable performance of the resultant heat exchanger, especially offlow of fluid e.g. air, around the outside of the tubes. The orientedtubes should be annealed or heat set at a temperature above the expectedoperating temperature of the resultant heat exchanger, in order toreduce the amount of distortion of the oriented tubes during use of theheat exchanger.

The fabrication of devices having oriented and expanded tubes has beendescribed above with reference to methods in which the tubes areoriented and subsequently expanded. However, the orientation step may becarried out in a manner that provides an oriented tube of requireddimensions without utilizing an expansion step i.e. the tubes areproduced in a single step. In an embodiment of such a single stepmethod, a rod or similar object having a diameter corresponding to thediameter of the tubes that is required after orientation, but not morethan about the diameter of the tubes prior to orientation, is insertedinto the tubes through at least the length of the tubes that will beoriented, the rod should have a length at least equal to the length ofthe tubes after orientation has occurred. The tubes are then oriented,e.g. in the manner described above, in which event the tubes areoriented but retain an internal diameter corresponding to the diameterof the rod. It is preferred that the rods be heated prior to theorientation of the tubes, as such heating assists in uniform heating ofthe polymer of the tubes prior to orientation. After suitable cooling ofthe tube the rod is removed and a device that has oriented tubes of adiameter corresponding to the diameter of the inserted rod is obtained;this method may be used to provide oriented tubes of the intended finaldiameter without involving any step of expanding tubes that havepreviously been oriented.

The uniformity of the heating of the article prior to orientation mayaffect the orientation process, especially the quality and uniformity ofthe oriented product. Convection ovens may be used, but it may bepreferable to use other heating methods e.g infra red heaters. Thetemperature of orientation of the polymer is preferably close to butbelow the melting point of the polymer. Subsequent to the orientation,the oriented article should be heat set or annealed e.g. by maintainingthe oriented article for a period of time at a temperature just belowthe temperature used in the orientation process.

FIG. 5 shows a comfort heat exchanger 14 in expanded view. Comfort heatexchanger 14 has a first manifold 15 and a second manifold 6 that areheld in spaced apart relationship by end panels 17, only one of which isactually shown. End panels 17 are of essentially the same length andwidth as the device of FIG. 4. A plurality of devices of FIG. 4 arelocated in side-by-side relationship between the two end panels 17,thereby essentially filling the space between the panels. Such devices,generally represented by 22, have end elements 18 and oriented andexpanded tubes 19. Devices 22 are arranged in side-by-side relationshipand are sealed together along junctions 21 in a fluid-impermeablemanner. End elements 18 have a plurality of orifices 20 therein, eachsuch orifice being in fluid-flow relationship with a tube 19. Manifolds15 and 16 are adapted to fit over the arrangement of end elements 18 toform a fluid-tight seal. First manifold 15 is shown as having a fluidinlet 23 and second manifold 16 is shown as having a fluid outlet 24.The flow of fluid 26 runs from an inlet section of the first manifold,through tubes to a second manifold, and then to an outlet section of thesecond manifold. Although the fluid inlet and fluid outlet are shown onopposing manifolds, the fluid inlet and the fluid outlet may be locatedon the same manifold, as shown in FIG. 6, an alternative form to FIG. 5provided that that manifold has means to direct the flow of fluid 26from the inlet which is 25, through some of tubes 19, which containexternal surface discontinuities 27 through the other manifold, throughthe remaining tubes 19 and to the fluid outlet.

The device of FIG. 5 is constructed in such a manner that fluid may bepassed through the heat exchanger 14 without loss of fluid due to leaksor the like.

In a preferred embodiment of the heat exchanger, spacers are inserted tomaintain the tubes in a desired position within the heat exchanger. Suchspacers are preferably fabricated from an elastomeric material e.g apolyetherester elastomer, examples of which are available under thetrademark Hytrel. One or more spacers may be placed in the heatexchanger. Examples of spacers include a sheet having holescorresponding to the size and location of the tubes; such a sheet may beslit in a number of ways to permit insertion of the spacer into the heatexchanger e.g. with parallel cuts through the holes of the sheet,starting from the same edge of the sheet or from alternating edges ofthe sheet, the latter producing a spacer that has a zig-zag shape priorto insertion into the heat exchanger.

In assembly of the heat exchangers of the invention, tube units with thehollow tube already oriented are bonded together in a side-by-siderelationship. Such bonding may be achieved using adhesives provided thatthe adhesive is capable of forming strong bonds with the polymer of theheat exchanger that do not permit leakage of fluid from the heatexchanger for extended periods of time. Alternatively, the tube unitsmay be heat sealed together using techniques similar to those used inthe so-called butt welding of polymer objects. For example, hot platesmay be brought into contact with the surfaces of two tube units that areto be sealed together so as to melt the surfaces. The molten surfacesare then rapidly brought into contact with each other, under pressure,and allowed to cool. Shims may be sealed between the tube units in thesame manner.

It is preferred that the walls of the tubes of the heat exchanger have athickness of less than 0.5 mm, and especially in the range of 0.12-0.4mm. It is to be understood, however, that although tubes having thinwalls are preferred, the walls must be of a thickness that will providethe physical properties required of the heat exchanger for the intendedend-use. The articles and devices described herein, which are intendedto be fabricated in steps for the manufacture of the heat exchangers,will have wall thickness that are proportionate to those given above,depending on the stage in the manufacture of the heat exchanger, orarticles or devices thereof.

For heat exchangers in the form of comfort heat exchangers, inparticular, it is preferred that the tubes of the heat exchanger have anoutside diameter in the range of 2-7 mm. However, for heat exchangersintended for other end uses, tubes of smaller or greater outsidediameter may be preferred.

In a preferred embodiment of the invention, the tubes have externalsurface discontinuities in the form of, for example, dimples,protrusions, matte or other roughened surfaces, in order to impartturbulence into fluid, especially air, flowing over the surface of theheat exchanger that is fabricated using the tubes. Similarly, internalsurface discontinuities would be advantageous, as shown in FIG. 6 (27),but are difficult to fabricate into the tubes using the techniquesdescribed herein. The turbulence imparted by the discontinuitiesfacilitates heat transfer between fluid and the material from which theheat exchanger is fabricated.

The comfort heat exchanger of the present invention is intended to bemanufactured from a thermoplastic polymer or a combination e.g. blend oralloy, of thermoplastic polymers. It is to be understood, however, thatthe manifolds and end panels, in particular, may be manufactured fromother materials. The tubed device is, however, manufactured as anintegral unit from a suitable thermoplastic polymer using an injectionmoulding process.

The thermoplastic polymers that may be used in the manufacture of thecomfort heat exchangers of the present invention will depend inparticular on the conditions under which the comfort heat exchanger isto be operated. Such conditions include not only the temperatures andpressures that are to be used and the required life of the exchanger,but also the type of fluids that are to be passed through the heatexchanger and around the heat exchanger. In the example of a heater foran automobile, the fluid passed around the heat exchanger is air,whereas the fluid passed through the heat exchanger is usually liquidfrom the radiator of the vehicle. Such liquid is comprised of water anda so-called anti-freeze e.g. ethylene glycol, but other additives e.g.anti-rust compounds and the like, may also be present in the liquid. Thepolymer should also be fatigue resistant, have a low creep modulus,provide a sufficiently rigid structure, and preferably be impactresistant.

A further requirement of the thermoplastic polymer used in themanufacture of the tubular portion of the heat exchanger is that thepolymer must be capable of being formed into the tubular portion as anintegral unit, of having the hollow tubes thereof oriented and, inembodiments, expanded to form the tube unit that is used in the assemblyof the heat exchanger.

In particularly preferred embodiments, the tubular portion of the heatexchanger is formed from a composition of a polyamide. The polyamideselected will depend primarily on the end use intended for the heatexchanger, as discussed above. In the case of use on a vehicle, the airpassed through the heat exchanger may at times contain salt or othercorrosive or abrasive matter.

Examples of polyamides are the polyamides formed by the condensationpolymerization of an aliphatic or aromatic dicarboxylic acid having 6-12carbon atoms with an aliphatic primary diamine having 614 12 carbonatoms. Alternatively, the polyamide may be formed by condensationpolymerization of an aliphatic lactam or alpha,omega aminocarboxylicacid having 6-12 carbon atoms. In addition, the polyamide may be formedby copolymerization of mixtures of such dicarboxylic acids, diamines,lactams and aminocarboxylic acids. Examples of dicarboxylic acids are1,6-hexanedioic acid (adipic acid), 1,7-heptanedioic acid (pimelicacid), 1,8-octanedioic acid (suberic acid), 1,9-nonanedioic acid(azelaic acid), 1,10-decanedioic acid (sebacic acid), 1,12-dodecanedioicacid and terephthalic acid. Examples of diamines are1,6-hexamethylenediamine, 1,8-octamethylene diamine, 1,10-decamethylenediamine and 1,12-dodecamethylene diamine. An example of a lactam iscaprolactam. Examples of alpha,omega aminocarboxylic acids are aminooctanoic acid, amino decanoic acid, amino undecanoic acid and aminododecanoic acid. Preferred examples of the polyamides arepolyhexamethylene adipamide and polycaprolactam, which are also known asnylon 66 and nylon 6, respectively.

As will be appreciated by those skilled in the art, the polyamidesdescribed above exhibit a wide variety of properties. For instance,meltinq points of polymers of dicarboxylic acid/diamine polymers willdiffer significantly from polymers of lactams or alpha,omegaaminocarboxylic acids and from copolymers thereof. Similarly, otherproperties e.g. permeability to fluids, gases and other materials willalso vary. Thus, even if the polymer selected is polyamide, a particularpolyamide may have to be selected for a particular end use.

In an embodiment of the present invention, the polyamide may be aso-called amorphous polyamide. The amorphous polyamide may be used asthe sole polyamide, or admixed with a polyamide of the type disclosedabove. It will be appreciated by persons skilled in the art thatamorphous polymers do not have glass transition temperatures, and thussuch polymers should be heated to a temperature below that at whichcreep may be significant but sufficiently high to permit uniformorientation of the tubes.

Although the present invention has been particularly described withreference to tubes formed from compositions of polyamides, it will beappreciated that a wide variety of polymers are potentially useful inthe fabrication of the tubes. The selection of such polymers will dependon a number of factors, as discussed above, especially the anticipatedoperating temperature of the heat exchanger, in order to obtain a heatexchanger with the properties required for operation under a particularset of operating conditions. Examples of polymers include polyethylene,polypropylene, polycarbonate, polyesters, polyphenylene oxide,polyphenylene sulphide, polyetherimide, polyetheretherketone, polyetherketone, polyimides, polyarylates and high performance engineeringplastics. Such polymers may contain stabilizers, pigments, fillers andother additives known for use in polymer compositions. The nature of thepolymer composition used may affect the efficiency of the heatexchanger, as it is believed that heat is capable of being dissipatedfrom the heat exchanger by at least both convection and radiation

Alloys and/or blends of polymers especially alloys and/or blends ofpolyamides may be used in the fabrication of the heat exchangers.

In use, it is possible that all or part of the fluid that is passedthrough the tubes of the heat exchanger will have a tendency to permeatethrough the walls of the tubes. Such permeation may result in unpleasantor other unacceptable odors being emitted from the heat exchanger and/orchanges in the composition of the fluid that are unacceptable withrespect to the continued operation of the heat exchanger and/or of thesource of the fluid. If the anticipated rate of permeation isunacceptable, all or part of the heat exchanger, especially the tubeportion of the heat exchanger may be coated with a barrier material e.g.a coating of polyvinylidene chloride. Any such coating may, for example,be applied by dip-coating the heat exchanger or by spray coating all orpart of the heat exchanger but should be of a type and thickness thatdoes not significantly adversely affect the operating effectiveness ofthe heat exchanger.

Heat exchangers of the present invention in the form of comfort heatexchangers are particularly intended to be used in automobiles and othervehicles. In use as a comfort heat exchanger in an automobile, the heatexchanger may have, for example, about 25-40 tubes across its width,which is typically about 20 cm. Examples of such heat exchangers areillustrated in the examples below.

The present invention is illustrated by the following examples:

EXAMPLE I

A tubular device substantially as illustrated in FIG. 1, but having 9tubes over the length of 6.3 cm of the device, was injection mouldedfrom polyhexamethylene adipamide. Pins were inserted into the tubes ofthe moulded device and then the device containing pins was placed in aneven at a temperature of 244° C. for a period of 30 seconds While stillin the oven, the tubes were oriented 3.2 times. The oriented device wasthen heat set at a temperature of 244° C. for 30 seconds and then placedin a freezer at a temperature of about -11° C. for about 5 minutes. Theresultant tube diameter was 0.33-0.35 cm and the wall thickness was0025-0.028 cm.

A series of the resultant tubular devices were welded together byheating the sides of the end elements of two tubular devices and thenbringing the heated surfaces into contact under pressure. Aninlet/outlet manifold was placed over one end of the welded tubeelements and a second manifold was placed over the other end, so thatfluid to be cooled would enter at the inlet, pass through tubes to theother manifold and then pass back through other tubes to the outletsection of the manifold. In this manner, a heat exchanger having 38tubes across its width and 9 tubes deep, spaced over a width of 15.2 cm,a height of 21 cm and a depth of 5.0 cm was fabricated; the heatexchanger was of a type intended for use as a comfort heat exchanger inan automobile.

Tests were conducted to determine the rate of heat exchange of thecomfort heat exchanger. Heated water was fed to the inlet of the heatexchanger. The temperature of the water was measured at the inlet andoutlet of the heat exchanger. Air was passed through the heat exchanger,and the air pressure drop across the heat exchanger was measured. Theresults obtained are given in Table I.

As a comparison, the same tests were carried out on a commercialautomobile comfort heat exchanger of the same dimensions and which hadbeen fabricated from metal; the commercial metal heat exchanger weighedapproximately 1.25 kg, compared with approximately 0.52 kg for the abovethermoplastic heat exchanger. The results obtained are also given inTable I.

                  TABLE I                                                         ______________________________________                                        Run No.*       1      2        3    4                                         ______________________________________                                        Air flow       2.83   2.83     5.66 5.66                                      (cu. meters/min.)                                                             Inlet air temp.                                                                              16.1   16.7     16.7 17.8                                      (°C.)                                                                  Pressure drop  12.7   6.35     61.0 12.7                                      (mm. water)                                                                   Water temp. (°C.)                                                      In             86.9   86.8     87.3 85.9                                      Out            84.6   84.2     82.1 81.1                                      Heat transfer                                                                 (Joules/min)   131k   146k     298k 272k                                      (J/hr. °C. itd**)                                                                      11k   125k     253k 240k                                      ______________________________________                                         *Runs 1 and 3 were made using the heat exchanger of the invention and Run     2 and 4 were the comparative runs.                                            **Joules/hour. °C. itd are units used in the automobile industry t     express the heat transfer of a heat exchanger; "itd" is inlet temperature     difference, defined as difference between the inlet water temperature and     the inlet air temperature.                                               

Although the pressure drop across the heat exchanger was higher for theheat exchanger of the invention, that heat exchanger gave similar orbetter heat exchange performance than the commercial heat exchanger.

EXAMPLE II

The procedure of Example I was repeated using heat exchangers of theinvention that had the same overall dimensions as that of Example Iexcept that there were either 28 or 31 tubes across the heat exchangerinstead of 38 tubes. The tubular devices were the same as in Example I,but in the assembly of the heat exchanger shims were placed between theend elements being welded together so that the desired number of tubesacross the heat exchanger was obtained. In addition, the heat exchangershad two spacers which were used to install and maintain the tubes in auniform pattern.

The results obtained are given in Table II.

                  TABLE II                                                        ______________________________________                                        Run No.*      5           6      7                                            ______________________________________                                        Air flow      2.83        4.24   5.66                                         (cu. meters/min.)                                                             Inlet air temp.                                                                             20.6        20.6   20.0                                         (°C.)                                                                  Pressure drop 3.30        6.86   13.0                                         (mm. water)                                                                   Water temp. (°C.)                                                      In            87.4        87.8   88.2                                         Out           85.2        85.0   84.3                                         Heat transfer                                                                 (Joules/min)  126k        157k   220k                                         (J/hour. °C. itd)                                                                    113k        140k   194k                                         ______________________________________                                        Run No.*      8           9      10                                           ______________________________________                                        Air flow      2.83        4.24   5.66                                         (cu. meters/min.)                                                             Inlet air temp.                                                                             18.9        19.4   18.9                                         (°C.)                                                                  Pressure drop 7.87        15.0   25.4                                         (mm. water)                                                                   Water temp. (°C.)                                                      In            88.5        88.1   87.9                                         Out           85.7        84.2   83.2                                         Heat transfer                                                                 (Joules/min)  157k        220k   267k                                         (J/hour. °C. itd)                                                                    135k        192k   232k                                         ______________________________________                                        Run No.*      11          12     13                                           ______________________________________                                        Air flow      2.83        4.24   5.66                                         (cu. meters/min.)                                                             Inlet air temp.                                                                             20.6        20.6   20.6                                         (°C.)                                                                  Pressure drop 6.09        9.91   15.7                                         (mm. water)                                                                   Water temp. (°C.)                                                      In            87.7        88.4   87.9                                         Out           83.5        83.2   80.9                                         Heat transfer                                                                 (Joules/min)  235k        298k   397k                                         (J/hour. °C. itd)                                                                    210k        264k   354k                                         ______________________________________                                         *Runs 5, 6 and 7 were made using the heat exchanger of the invention          having 28 tubes.                                                              *Runs 8, 9 and 10 were made using the heat exchanger of the invention         having 31 tubes.                                                              *Runs 11, 12 and 13 were comparative runs, using the metal heat exchanger                                                                              

The lower number of tubes significantly reduced the effectiveness of theheat exchangers of the invention. Examples I and II show that asignificant variation in efficiency is achievable by changes in designof the heat exchangers.

EXAMPLE III

In an alternate embodiment, tubular devices injection moulded frompolyhexamethylene adipamide have been subjected to an orientationprocess in the presence of infra red heaters instead of an oven. Pinswere inserted into the tubes and the pins were then heated for a periodof time. The tubular devices containing the heated pins were then placedbetween infrared heaters for a further period of time, after which thetubes were oriented. The resultant oriented devices were then heat set,cooled to ambient temperature and placed in a freezer for a furtherperiod of time.

Further details of experimental conditions that have been used are givenin Table III.

                  TABLE III                                                       ______________________________________                                        Pin diameter    3.00   2.75     2.50 2.00                                     (mm)                                                                          Pin heating time                                                                              90     70       50   50                                       (sec)                                                                         Tube heating time                                                                             100    70       30   18                                       (sec)                                                                         Tube temperature*                                                                             182    182      153  153                                      (°C.)                                                                  ______________________________________                                         *The tube heating temperature was measured by a thermocouple placed           adjacent to the tubes being heated.                                      

The oriented tubular devices were heat set at 208° C. for 45 seconds,placed in air at 22° C. for 50 seconds and then in a freezer at -11° C.for 5 minutes.

This procedure has been found to offer some advantages with respect todecreased amounts of distortion obtained in the oriented tubular devicesthat are obtained.

We claim:
 1. A device manufactured from a thermoplastic polymer, saiddevice essentially comprising a plurality of transverse parallel hollowtubes integrally connected by a radiused and flared integral junction ateach end to a substantially rigid end element, each of said end elementshaving planar sides and opposing faces, the tubes being internallyconnected to one face of each end element, said end elements havingorifices therein extending between said opposite faces and being influid flow communication with said hollow tubes, and the hollow tubeshaving been oriented to increase the length thereof by at least twotimes and to obtain an internal diameter of at least 0.5 times that ofthe tubes prior to orientation, the walls of said tubes between theintegral junctions being of substantially uniform thickness.
 2. Thedevice of claim 1 in which the hollow tubes have been oriented toincrease the length thereof by at least two inches and then expanded sothat the internal diameter of said tubes is at least 0.5 times thediameter of the tubes prior to orientation.
 3. The device of claim 1 inwhich the thermoplastic polymer is a polyamide.
 4. The device of claim 3in which the polyamide is polyhexamethylene adipamide.
 5. The device ofclaim 3 in which there are 4-10 tubes.
 6. A heat exchangercomprising:(a) two manifold elements, said manifold elements beingadapted to receive and discharge a fluid, and (b) a plurality of tubeunits transversely located between said manifolds, each said tube unitsbeing formed from thermoplastic polymer and essentially comprising aplurality of transverse parallel hollow tubes integrally connected by anintegral junction at each end to a substantially rigid end element, eachof said end elements having planar sides and opposing faces, the tubesbeing integrally connected to one face of each end element, each of saidtubes being radiused at the integral junction of tube and end element,said end elements having orifices therein extending between saidopposite faces and being in fluid flow communication with said hollowtubes, the hollow tubes having been oriented to increase the lengththereof by at least two times, the walls of said tubes between theintegral junctions being of substantially uniform thickness, said tubeunits being positioned so that the hollow tubes are in a spaced apartbut juxtaposed relationship, said tubes units being sealed together sothat fluid will flow from one manifold to the other manifold through thehollow tubes.
 7. The heat exchanger of claim 6 in which the integraljunctions are radiused and flared.
 8. The heat exchanger of claim 7 inwhich the internal diameter of the oriented tubes is at least 0.5 timesthat of the tubes prior to orientation.
 9. The heat exchanger of claim 7in which the hollow tubes have been oriented to increase the lengththereof by at least two times and then expanded so that the internaldiameter of said tubes is at least 0.5 times the diameter of the tubesprior to orientation.
 10. The heat exchanger of claim 7 in which thethermoplastic polymer is a polyamide.
 11. The heat exchanger of claim 10in which the polyamide is polyhexamethylene adipamide.
 12. The heatexchanger of claim 10 in which there are 4-10 tubes in each tube unit.13. The heat exchanger of claim 12 in which there are 25-40 tube units.14. The heat exchanger of claim 10 in which the thickness of the wallsof said tubes is less than 0.5 mm.
 15. The heat exchanger of claim 14 inwhich the thickness is in the range of 0.12-0.4 mm.
 16. The heatexchanger of claim 15 in which the outside diameter of the tubes is inthe range of 2-7 mm.
 17. The heat exchanger of claim 10 in which theheat exchanger is adapted so that fluid will flow from an inlet sectionof a first manifold, through tubes to a second manifold, and then backthrough further tubes to an outlet section of the first manifold. 18.The heat exchanger of claim 10 in which the tubes have external surfacediscontinuities.